In recent years, an optical disc device such as a CD (Compact Disc) for reproducing music and a DVD (Digital Versatile Disc) for reproducing image has widely spread in order to record large amount of data. In these days, the HD DVD (High Definition Digital Versatile Disc) and the BD (Blue-Ray Disc) have appeared as next-generation DVDs allowing long time reproduction of high-definition images. In an optical disc medium used for these optical disc devices, digital data of music and image are recorded on a data recording surface in a spiral shape as a line of fine record markings. An optical disc device reads the line of fine record markings and reproduces the recorded digital data.
The optical disc device irradiates focused laser light from an optical head to the data recording surface of the optical disc medium whose rotation is controlled by a spindle motor. The optical head includes a laser diode (LD), optical elements, and mechanism for moving laser light in a vertical direction (focusing) and in a radial direction (tracking) to a disc surface. The optical head detects reflected light from the data recording surface of an optical disc medium and is controlled by a focusing and tracking movable mechanism so as to constantly scan the record marking line. The reflected light of a light irradiated to the record marking line is detected by a light detector based on contrasting or polarization and is converted into a reproduction signal being an electric signal. A synchronous clock is extracted by a PLL (Phase Locked Loop) circuit from the reproduction signal detected by the optical head, and simultaneously the reproduction signal is formed to be a pulsed shape based on the synchronous clock. After that, error correction and other processing are performed and music, video, or the like is reproduced.
On the other hand, when recording data on an optical disc medium, the laser light modulated in accordance with user data is irradiated on the data recording surface with a stronger power than that in the reproduction to change a physical property (such as a reflectance and a magnetization direction of a magnetic domain) of micro regions on a recording surface of the optical disc medium. For a recordable CD or DVD medium, a disc medium is employed whose grooving track is wobbled (meandering) in the radial direction. A record timing signal is generated based on this wobbling. A wobbling frequency is required to be higher than the following frequency band of the tracking servo and to be in a low frequency which does not affect the reproduction RF signal. For example, one 192nd of an RF channel frequency is selected as the wobbling frequency for the CD, one 186th of the RF channel frequency for the DVD-R, DVD-RW, and DVD-RAM, and one 32nd of the RF channel frequency for the DVD+R and DVD+RW.
The condition of the wobbling can be detected from the differential (a radial push-pull signal) between two outputs which are respectively outputted by two light detectors arranged in the radial direction detecting the reflected lights from the optical disc medium. The detected signal will be hereafter referred to as the “wobble signal”. A recording clock signal synchronized with the wobble signal is generated by a multiplying PLL circuit, and the user data is recorded on the optical disc medium in synchronism with timing of the recording clock signal. Accordingly, even when an eccentricity of the disc or uneven rotation of the disc occurs, the data can be seamlessly recorded at an accurate position on the optical disc medium. Furthermore, address information can be read from the wobble signal by previously forming the wobble for physical position (address) data on the optical disc medium through a phase modulation or a frequency modulation. Thus, recording, additional recording, or overwriting can be executed from any position of the optical disc medium.
The modern optical disc device generally performs the recording on a removable medium, which is different from magnetic disc devices. Further, in order to reduce cost, the medium is not usually protected by a cartridge or the like. For this reason, there is a high possibility of a micro defect because of a scratch and/or dust on the medium surface, in addition to defects that may occur in disc producing. In consideration of this point, the optical disc device performs a strong product code error correction. But sometimes the optical disc device fails to correct the defect depending on the size or frequency of the defect. In the reproduction, it is often possible to mitigate for the defect by disc cleaning so that the medium can be reproduced. However, when recording on the defected medium, the data cannot be recorded because the defect prevents a thermal control. For this reason, defect management in the recording is highly relevant for enhancing the reliability of the optical disc device. The defect management in the recording is generally performed in a following procedure.
(1) Recording data;
(2) Interrupting the recording after a certain period;
(3) Seeking a record starting position;
(4) Reproducing the recorded area;
(5) Seeking a next recording position when the reproduction can be normally performed and returning to (1), or registering the area in a list as a defect area;
(6) Seeking a substitution area;
(7) Recording data in the substitution area;
(8) Seeking a head of the substitution area;
(9) Reproducing data recorded in the substitution area; and
(10) Seeking a next recording position when normally reproduced and returning to (1).
As described above, a lot of time is required since the seeking for verifying the recording state and the disc rotation waiting occurs, resulting in degradation of throughput in the recording. The throughput can be enhanced when a plurality of heads is mounted, as in the case of magnetic disc devices. However, the cost of an optical head mounting optical components is high so that this fashion is difficult to be employed. In addition, it is also one factor that the optical head is heavy and requires long times for seeking and the like. It is difficult to perform the defect management and the substitution recording with interrupting the recording in midstream, especially when data such as subsequently flowing large video data is recorded.
Next, a read signal outputted from the optical head in a case where defects exist on an optical disc medium will be explained. To read the user data recorded in an optical disc medium, the optical disc device produces a reproduction signal allowing detection of difference of a physical state (for example, a reflectance) in a recording area by performing a certain kind of processing (calculation with separately arranged light detectors and the like) on the reflected light from a surface of the recording medium. Normally in the recording, since a physical state on the medium surface is changed by controlling the temperature in an area where laser light is focused, it is difficult to judge the recording state by monitoring a reproduction signal in recording. On the other hand, the wobble signal can be adequately detected in the recording as can be known from a fact that the recording clock signal can be generated in the recording. However, the wobble signal deteriorates when passing the defective area. For example, the amplitude of the wobble signal is reduced in a portion where a scratch or dust exists and an amplitude variation (which is increased in some cases) or phase disturbance occurs in a portion where a fingerprint or contamination is stuck.
In a case of passing such a defective area, the seeking and the rotation waiting have occurred since the recording was interrupted and a recording area is reproduced. However, the recording can be continued without seeking and the like if a recording quality can be judged in the recording process. As a conventional method for detecting a defect in the recording process, Japanese Laid-Open Patent Application JP-P2000-322741A discloses a method for example. In this method, it is detected in the recording that the wobble signal lacks for a certain period or that a cycle of the wobble signal is continuously lying out of the predicted cycle for a certain period and then defect replacement processing is performed. That is, it is judged by capturing deterioration of the wobble signal in recording process whether a defect exists or not.
In this method, the existence or absence of defects is judged based on a wobbling cycle. Therefore, in an optical disc medium whose cycle changes because of the modulation, an error judgment occurs. As such optical disc medium, DVD+R/RW, a CAPA (Complementary Allocated Pit Address) area of the DVD-RAM, HD DVD and BD are given. In addition, in the case that a defect is observed such that the frequency of the wobble signal is approximately constant but the phase of the wobble signal is largely shifted, the defect cannot be determined as a defect. Moreover, there also is a case where the wobble signal is not completely lacked and its amplitude is reduced or increased. In the above method, such a defect cannot be detected.
Furthermore, Japanese Laid-Open Patent Application JP-P2002-230752A discloses a method for generating a window of the cycle of the wobble signal in response to an output of the PLL circuit which generates a signal synchronizing the wobble signal and for performing defect detection in recording process based on whether or not an edge of the wobble signal exists in the window. FIG. 1 shows the configuration of this wobble defect detection device which includes a PLL circuit 101, a wobble window signal generation section 103, a wobble lock/unlock detection section 105, and a wobble defect detection section 107. When a wobble signal is applied, the PLL circuit 101, based on the wobble signal, outputs a wobble clock signal Wbclk corresponding to a reproduction clock or a channel clock and outputs a wobble signal PWB to which the PLL (Phase Locked Loop) is applied. The wobble window signal generation section 103 generates a window signal including a condition of a window width based on the applied wobble signal to which PLL is applied. The window width is set on a basis of the number of the wobble clock signals Wbclk given from a system control section. The wobble lock/unlock detection section 105 detects a lock state/unlock state on the basis of the set wobble lock condition and a set wobble unlock condition. When the number of the wobble signals which are not detected in a wobble window interval meets a defect determining condition in units of blocks or sectors, the wobble defect detection section 107 recognizes it as a wobble defect and outputs a wobble defect detection signal.
As described above, since the wobble defect detection device judges a phase shift with the PLL clock, an error judgment occurs in a recording medium whose wobble is phase-modulated similar to the above mentioned method. In addition, there is a problem that a defect causes an amplitude variation of the wobble signal that cannot be detected.
In Japanese Laid-Open Patent Application JP-A-Heisei, 10-269716, address information called ATIP (Absolute Time In Pre-groove) embedded in the wobble signals of CD-R/RW is read. It is judged whether or not an error of the information exists based on CRC (Cyclic Redundancy Code) added to this information, and defect detection is performed in recording process based on the judgment. In this technique, its range can be enlarged to the application for the DVD so that the judgment can be performed based on parity bits in an ADIP (ADress In Pre-groove) of the DVD+R/RW, an LPP (Land Pre-Pit) of the DVD-R/RW, and the CAPA of the DVD-RAM. However, in such distributed pre-pit, there is a problem that a defect locally existing in units of sectors cannot be detected for example.
In addition, Japanese Laid-Open Patent Application JP-P2004-348800A discloses a data reproduction device which reproduces wobble signals from a disc whose recording track is wobbled and determines a scratch on the disc. This data reproduction device includes reading means, wobble signal detecting means, A/D converting means, frequency analyzing means, and scratch estimating means. The reading means reads data from the record track and the wobble signal detecting means detects the wobble signal from the data. The A/D converting means converts the detected wobble signal into a digital signal. The frequency analyzing means performs frequency analysis on the digitized wobble signal. The scratch estimating means outputs a scratch determination signal by determining a scratch on the disc based on a result of the frequency analysis.
Japanese Laid-Open Patent Application JP-A-Heisei, 6-187654 discloses a defect detection circuit of an optical disc device. This defect detection circuit includes a wobble signal detection circuit and a gate circuit. In recording or reproducing the optical disc where a pre-groove of a wave form is inscribed to a track groove, the wobble signal detection circuit detects existence or absence of the wobble signal obtained from the wave form. The gate circuit permits a passage of a signal showing the absence of the wobble signal from the wobble signal detection circuit. The defect detection circuit is configured so as to output a defect signal when the wobble signal disappears at time other than track searching through controlling a gate based on a signal indicating that the track searching is currently processed.